The present invention relates to an asphalt heating unit for heating existing asphalt pavement to a temperature sufficient to provide a bonding of newly laid asphalt and previously laid asphalt at speeds comparable to the speed of an asphalt paver, thereby permitting the fusing or bonding of new asphalt material from an asphalt paver with existing, previously laid asphalt pavement.
During asphalt paving operations, it is frequently necessary to apply a lift or mat of new hot asphalt adjacent to existing cold asphalt pavement which has been laid possibly a few days or a week beforehand. The joining line between the hot asphalt and cold asphalt is sometimes referred to as a seam or joint, and is viewed as an inherent weak point in the pavement subject to premature failure. Frequently, the existing asphalt has accumulated dirt and stone dust on its surface which, together with the difference in temperature of the hot and cold asphalt, prevents a proper bonding of the new and old asphalt at the seam. This joint or seam problem is a significant one confronting the asphalt paving industry, whether the asphalt paving application is for roads, parking lots, airport runways or taxiways, for example.
One approach to minimize this problem has been to stagger the seams of the various courses of asphalt. In typical asphalt paving, a binder course is first laid over a roadbed, and this binder course has a thickness on the order of several inches. If the asphalt paving machine is set to lay asphalt 10 feet in width, for a 20-foot roadway a seam will appear in the center of the roadway at the crown of the road. A second or wear course is applied on top of the binder course, but the middle seam of this wear course may be staggered relative to the seam of the binder course. However, even with the staggered seam method, the top seam still exists and provides an inherent weak point whereby the seam tends to enlarge and separate after one or two seasons of use. As soon as a separation in a seam occurs, it gradually increases in width due to the constant thawing and freezing of water during inclement weather and the hydraulic pumping action from constant traffic flow, which causes the asphalt to break out and leave large cracks and holes in the asphalt pavement.
While attempts have been made to heat the edge of the cold asphalt pavement or lift in preparation for laying a screed of hot asphalt adjacent to the previously laid asphalt, these attempts have met with limited success.